The disclosed embodiments generally relate to a navigation system and more particularly to a relative navigation measurement system for vehicle and terrain relative navigation and control.
In-space rendezvous is a key enabling technology for many current and planned space missions, especially in the areas of human exploration, multiplatform scientific investigations, and in-space servicing. Having an ability to rendezvous with an orbiting spacecraft in order to provide refuel, repair, and repositioning services, is significant. However, earlier launched space vehicles may be characterized as non-cooperative, that is, they may have no cooperative retro-reflectors, acquisition sensors, or docking or grapple features. Furthermore, some form of robotic manipulator may be required to capture a suitable feature, such as a target vehicle's Marman ring, the location where the target vehicle structure connects with a launch vehicle. In addition, capturing a target space vehicle generally requires a high level of autonomy because of the size, mass, and relative motion of the vehicle.
Optical imaging systems may provide images with adequate resolution for roughly locating a target vehicle but may not provide range detection with the accuracy required to precisely align the target and a capture device such as a robot manipulator. Also, optical image quality may vary significantly depending on the orientation of the sun or other bright bodies relative to the target vehicle. Three dimensional imaging sensors, such as Light Detection and Ranging (LiDAR) systems, may supply their own sources of illumination and may therefore produce range information and imagery independent of natural lighting but may not provide enough resolution to accurately align the target vehicle and capture device.
Various solutions may be used to translate between the coordinate system of the capture device and the target vehicle and to register 3-D shapes of the target vehicle in order to autonomously estimate the target vehicle's relative attitude and position, also referred to as the target vehicle's pose. For example, Horn, “Closed-form Solution of Absolute Orientation Using Unit Quaternions,” Optical Society of America, April 1987, pp. 629-642, Vol. 4, No. 4, provides a closed form solution to the least-squares problem for three or more points. As another example, Besl and McKay, “A Method for Registration of 3-D Shapes,” IEEE Transactions on Pattern Analysis and Machine Intelligence, February 1992, pp. 239-256, Vol. 14, No. 2, describes a general purpose method for the accurate and computationally efficient registration of 3-D shapes including free-form curves and surfaces. However, these theoretical solutions alone do not provide pose estimation solutions, in particular at a rate and accuracy required for acquiring a target vehicle.
It would be advantageous to provide a relative navigation measurement system that overcomes these and other disadvantages.